1. Field of the Invention
The present invention relates to a battery and a method of manufacturing the same.
2. Description of Related Art
Various types of batteries have been developed in recent years. For example, a nickel-metal hydride storage battery has rapidly come into wide use as a secondary battery with a high energy density and a high reliability.
This nickel-metal hydride storage battery has been known as e.g. a rectangular sealed nickel-metal hydride storage battery comprising an electrode plate assembly that includes a plurality of positive electrode plates and a plurality of negative electrode plates alternately laminated with separators interposed one by one between them, and a rectangular parallelepiped battery case containing the electrode plate assembly (e.g., JP-A-2001-313066, JP-A-2001-93505, and JP-A-2002-260719).
In the above nickel-metal hydride storage battery, the positive electrode plate includes for example a positive electrode plate produced in a manner that a positive electrode substrate made of foamed nickel (made by plating nickel on a skeleton surface of an urethane foam and then burning the urethane foam) is filled with a positive mix material containing a positive active material and so on. Further, the negative electrode plate includes for example a negative electrode plate produced in a manner that a negative mix material containing a hydrogen absorbing alloy and so on is filled in pores of a negative electrode substrate made of a nickel-plated steel plate and also coated on both surfaces of the negative electrode substrate. The electrode plate assembly includes for example an electrode plate assembly produced in a manner that a plurality of the positive electrode plates and a plurality of the negative electrode plates are alternately laminated with separators interposed one by one between them.
Meanwhile, the aforementioned positive electrode plates and negative electrode plates would not easily be formed in flat shape, which may be curved or warped. Thus, the positive and negative electrode plates constituting the electrode plate assembly include curved plates and uncurved plates, which are laminated with respective curves facing to opposite sides, resulting in an uneven distance between adjacent positive and negative electrodes. For instance, when such positive and negative electrodes expand or swell after repeated charge and discharge, each separator interposed therebetween may be compressed and, in particular, locally highly pressurized in a region where the opposite curves of the adjacent positive and negative electrode plates face to each other. In the region in which the separator is locally strongly compressed, the distance between the adjacent positive and negative electrode plates is short. This may deteriorate an insulation property of the separator between the positive and negative electrode plates, thus inducing a short circuit.